As Sarah Palin braces for her vice-presidential debate tonight with Joe Biden, a new TIME poll shows the Alaska Governor is surprisingly unpopular among likely women voters.

Overall, Palin is viewed favorably by 47% of likely voters and unfavorably by 40%. But her numbers are worse among women than men: 45% of all women surveyed have a negative opinion of Palin, compared to 42% who view her positively. Fifty-two percent of men have a favorable opinion, while 35% are in the unfavorable camp.

Those numbers do not compare well with those of her direct competitor in the general election, Joe Biden. Among women, the Democratic candidate for vice president is viewed positively by 51% and negatively by 27%. Biden has an overall favorable to unfavorable split of 50%-31%, while McCain's is 54%-38% and Obama's rests at an enviable is 60%-33%.

Palin's unpopularity with women may prove a drag on the ticket with the very constituency she initially inspired. Obama now leads McCain by 17 points among likely female voters, 55%-38%. Just after the Republican convention, a TIME poll had the two candidates virtually tied among women, 48% for Obama and 47% for McCain.

The poll of 1,133 likely voters was conducted Sept. 26-29 and has a margin of error of +/- 3 percentage points.

Palin has perhaps her best opportunity of the campaign to reverse her slide tonight. A strong showing could convince women that she represents a historic opportunity to break the political glass ceiling. And expectations for her performance couldn't be much lower; after her unsteady performance in interviews with Katie Couric (including an apparent inability to name any Supreme Court cases other than Roe v. Wade that she disagreed with), Palin could go a long way to restoring her credibility with a strong showing in an unstructured format.

Biden and the Democrats, meanwhile, will continue to try and exploit Palin's troubles with voters  especially women. In his own interview with Couric, Biden responded to the same question about disagreements with the Supreme Court by targeting a key issue for women: domestic violence.

Biden, who for years chaired the Senate Judiciary committee, went on at length about his authorship of the Violence Against Women Act and how the Court had ruled against him on a particular provision. Expect to see more of that tonight at the debates.